If you replace the cluster you will have a tamper dot. In the cluster the mileage is stored and the VIN number. If the replacement cluster has a higher mileage it will show the higher mileage.
Also keep in mind that a used cluster, even if it's the same partnumber might not be programmed for your specific car, for example a 6 or a 4 cylinder engine. So you need to program your Car's specific functions into the used cluster
Depending on the chipset used inside of the cluster you can or cannot change the Mileage using PA Soft - BMW Scanner 1.4 and VIN via NCS Expert.
If you have the M35090 chipset like I have you need to disassemble the cluster and either replace or program the old chipset, it's called "virginize" a cluster. I am now in the middle of the process of trying to "virginize" a spare cluster and get that all working with my Z.